The present invention relates to improvements in a method for forming a developer layer by which the thickness of the developer layer held and carried on the surface of a developer carrying member is regulated in a developing means to be used to develop a latent image formed on the surface of a photoreceptor drum or belt in electrophotography.
Further, the present invention relates to a contact or a non-contact developing method by which an electrostatic latent image on an image carrier is developed with a one-component or two-component developer.
In an electrophotographic image forming apparatus in which one-component or two-component developer is used, it is necessary to maintain the thickness of a developer layer formed on a developer carrying member (which is also referred to as a developing sleeve) to be thin and uniform in order to obtain images of high quality.
Conventionally, the thickness of a developer layer is regulated by a fixed regulating plate. However, in the case of the conventional fixed regulating plate, the assembling accuracy is limited when the developer carrying member and the fixed regulating plate are assembled, the reduction of eccentricity of the developer carrying member is limited, and further the accuracy of a bearing provided to the developer carrying member is limited. Therefore, the thickness of the developer layer can be reduced to 0.3 mm at the minimum.
According to the aforementioned conventional method, it is difficult to obtain a uniformly thin developer layer. In order to obtain a thin uniform layer, various developer layer thickness regulating apparatus other than the fixed regulating plate have been devised. For example, the following apparatus have been devised.
(a) The developer layer forming apparatus described in the official gazette of Japanese Patent Application Open to Public Inspection No. 43038-1979 is structured in such a manner that: in the case of a one-component toner, a developer layer thickness regulating member which is composed of a sheet-shaped resilient member, one of which is free, is bent and contacted with a developer carrying member with pressure.
(b) The developer layer forming apparatus described in the official gazette of Japanese Patent Application Open to Public Inspection No. 51848-1979 is structured in such a manner that: a plate-shaped resilient member is used in which a metallic spring and a soft resilient member are laminated; and the thickness of one-component developer layer is regulated when the loop portion of the soft resilient member is contacted with a developer carrying member with pressure.
(c) The developer layer forming apparatus described in the official gazette of Japanese Patent Application Open to Public Inspection Nos. 126567-1984 and 129879-1984 is structured in such a manner that: in a developing unit in which a one-component developer is used, a resilient roller is intermittently or continuously contacted with a developer carrying member so that a nip can be formed between them so as to regulate the developer layer thickness.
(d) The developer layer forming apparatus described in the official gazette of Japanese Patent Application No. 12627-1985 is structured in such a manner that: in a developing unit in which a one-component developer is used, a rotating roller is contacted with a developer carrying member composed of a resilient member so that the developer layer thickness can be regulated.
(e) Concerning a developer layer thickness regulating device which is applied to a two-component developer, the official gazettes of Japanese Patent Application Open to Public Inspection Nos. 191868-1987 and 191869-1987 have disclosed a technical means in which a thin developer layer is formed on a developer carrying member appropriate for non-contact development. This developer layer thickness regulating means is composed in such a manner that: one end of a resilient plate is supported by a support member and the other is directed toward the upstream side of developer flow on a developer carrying member; and the resilient plate is contacted with the surface of the aforementioned developer carrying member with pressure so that the layer thickness of developer including magnetic carrier and toner can be regulated. In the manner explained above, the developer layer thickness can be set thin more accurately than conventional regulating means.
(f) In the case of developing units in which a two-component developer is used, the official gazettes of Japanese Patent Application Open to Public Inspection Nos. 189582-1986 and 75563-1987 have disclosed a developing unit which is composed in such a manner that: a fixed plate-shaped layer thickness regulating member is provided; a magnetic member is disposed on the back of the aforementioned layer thickness regulating member; and the magnetic member is attracted by a fixed magnet provided inside a developer carrying member so that the loop portion or edge portion of the regulating plate can be pushed and contacted with the developer carrying member.
(g) The official gazettes of Japanese Patent Application Open to Public Inspection Nos. 50184-1990 and 64674-1990, and the official gazette of Japanese Utility Model Application No. 14159-1990 by the applicant, have disclosed a developing unit in which a developing amount regulating member (a thin layer rod) is provided in such a manner that it is opposed to a magnet fixed inside the developer carrying member and the aforementioned developer amount regulating member is contacted with the developer carrying member with pressure.
(h) The official gazettes of Japanese Patent Application Open to Public Inspection Nos. 282578-1989 and 283577-1989 have disclosed a developing unit in which the shape and size of the aforementioned developer amount regulating member are specified.
The disadvantages of the aforementioned conventional developer layer forming apparatus will be explained as follows: In the cases of (a) and (b), the developer layer thickness regulating member composed of a resilient member is bent, and the generated force is utilized to regulate the layer thickness. Therefore, the generated contacting force tends to be varied by the fluctuations of the rotating speed of the developer carrying member, the contacting position and the developer thickness, and further the contacting force tends to oscillate. Furthermore, countermeasures are not taken against the oscillation. Accordingly, the layer thickness regulating member resonates with a vibration generated in the image forming apparatus. Therefore, it is difficult to obtain a developer layer of a uniform thickness. Especially, in the case of apparatus (b), a soft resilient member is contacted with the developer carrying member, so that the above-described tendency is remarkably displayed. Further, the geometric shape of the nip portion is subjected to an irregular motion due to the fluctuations of the developer carrying member rotating speed, the contacting position, and the developing layer thickness, so that the area of the nip is varied. Accordingly, a problem is caused in which the thickness of the developer layer is not uniform. Other than the aforementioned inconvenience, when the nip is composed of a soft resilient member, clogging occurs in the nip due to developer, and further when the soft resilient member becomes worn out, a secular change occurs in the nip. The above-described problems tend to occur when a developer including hard material such as magnetic material and a fluidizing agent, is utilized.
A layer obtained by the apparatus of (c) and (g) is more stable and uniform than that obtained by the apparatus of (a). However, in the apparatus of (c) and (g), the layer thickness is regulated by a rotating member, so that the performance of the layer thickness regulating means of (c) and (g) is inferior in terms of releasing or eliminating the aggregated developer particles, so that the aggregated particles pass through the nip. Accordingly, even when an intermittent operation is conducted, a satisfactory performance can not necessarily be obtained, and image soilage and black spots are caused, so that the image quality is deteriorated. Further, in the case of the aforementioned layer thickness regulating means, contacting pressure must be balanced, so that the rotating and contacting mechanisms become complicated.
In the apparatus of (a)-(d) and (g), the contacting area of the layer thickness regulating means is relatively large, so that the following inconvenience is caused: in the case of a usual developing unit in which the amount of developer supplied to the nip varies momentarily, the developer layer thickness is influenced by the variation of the amount of developer supplied to the nip.
In the cases of (c) and (d), a developer carrying member preferable for one-component non-magnetic developer is provided with resilience, and a developer layer thickness regulating member is contacted with the developer carrying member with pressure so that a thin developer can be formed. In this case, the developer carrying member tends to be permanently deformed, and the elastic modulus of the developer layer thickness regulating member tends to vary when it is used over a long period of time, so that a thin developer layer can not be stably formed.
In the case of apparatus (e) which has been developed for two-component developer, the apparatus can not maintain performance satisfactorily when it is utilized over a long period of time.
In the apparatus of (a), (b), (e), (f), (g) and (h), a resilient developer layer thickness regulating plate is contacted with a rigid developer carrying member (which is a metallic developer carrying member) with pressure, so that a thin developer layer is formed. When the aforementioned apparatus is used over a long period of time, the elastic modulus of the resilient plate is varied, and the shape of the plate is permanently deformed, so that the durability of the layer thickness regulating member is short. Further, even when the resilient plate is displaced a little from the correct position in the process of assembly, the play provided to the edge of the resilient plate and the contacting force are varied, so that it is difficult to regulate the layer thickness stably. Therefore, this apparatus is disadvantageous in that: when the layer thickness regulating means is assembled in mass-production, the accuracy must be severely maintained.
In the case of apparatus (f), toner aggregation can be released by the interaction between a magnet provided on the back of the developer layer and that provided inside the developer carrying member. However, attraction force is activated through a solid-plate-shaped regulating member. Accordingly, when the distance between the magnets is increased, the attraction force is sharply decreased, so that the contacting force is lowered, that is, contacting force is fluctuated by the variation of the distance between the magnets. Therefore, the developer layer can not be stably pressed by the layer thickness regulating member so as to form a uniform layer, and the aggregation of toner or developer passes through the thickness regulating member. On the contrary, a constant layer thickness can not be obtained, and clogging occurs, so that white streaks are caused in the obtained image which deteriorate the image quality.